Decoupling the Effect of Shear Stress and Stretch on Tissue Growth and Remodeling in a Vascular Graft

Abstract

The success of cardiovascular tissue engineering (TE) strategies largely depends on the mechanical environment in which cells develop a neotissue through growth and remodeling processes. This mechanical environment is defined by the local scaffold architecture to which cells adhere, that is, the microenvironment, and by external mechanical cues to which cells respond, that is, hemodynamic loading. The hemodynamic environment of early developing blood vessels consists of both shear stress (due to blood flow) and circumferential stretch (due to blood pressure). Experimental platforms that recapitulate this mechanical environment in a controlled and tunable manner are thus critical for investigating cardiovascular TE. In traditional perfusion bioreactors, however, shear stress and stretch are coupled, hampering a clear delineation of their effects on cell and tissue response. In this study, we uniquely designed a bioreactor that independently combines these two types of mechanical cues in eight parallel vascular grafts. The system is computationally and experimentally validated, through finite element analysis and culture of tissue constructs, respectively, to distinguish various levels of shear stress (up to 5 Pa) and cyclic stretch (up to 1.10). To illustrate the usefulness of the system, we investigated the relative contribution of cyclic stretch (1.05 at 0.5 Hz) and shear stress (1 Pa) to tissue development. Both types of hemodynamic loading contributed to cell alignment, but the contribution of shear stress overruled stretch-induced cell proliferation and matrix (i.e., collagen and glycosaminoglycan) production. At a macroscopic level, cyclic stretching led to the most linear stress-stretch response, which was not related to the presence of shear stress. In conclusion, we have developed a bioreactor that is particularly suited to further unravel the interplay between hemodynamics and in situ TE processes. Using the new system, this work highlights the importance of hemodynamic loading to the study of developing vascular tissues.

Supramolecular Antifouling Additives for Robust and Efficient Functionalization of Elastomeric Materials: Molecular Design Matters

“…Electrospinning of these bisurea elastomeric materials yields fibrous and porous constructs, and when deposited on a rotating mandrel can be readily fabricated into tubular vascular grafts and heart valves …”

Humanin vitromodel of material-driven vascular regeneration reveals how cyclic stretch and shear stress differentially modulate inflammation and tissue formation

“…(2.8 mm outer diameter) as previously described. [33] The scaffold microarchitecture (i.e., fiber morphology, diameter, and organization) was assessed from scanning electron microscopy (SEM) images (Quanta 600F; FEI, Hillsboro, OR) and the scaffold mechanical properties were characterized from biaxial stress-strain curves (CellScale Biomaterial Testing, Waterloo, Canada) as described below. Prior to cell seeding, the silicone-mounted scaffolds were Human vena saphena cell culture: HVSCs were isolated from a single human donor after coronary by-pass surgery conforming to well-established protocols, [66] in accordance to the Dutch advice for secondary-use material.…”

“…The applied stretches were monitored and quantified from the minimum and maximum outer diameter of the scaffolds, using time-lapse photography and custom Matlab scripts (Matlab R2017; The Mathworks, Natick, MA). Shear stress was maintained at ~1 Pa by tuning the flow rate magnitude to 60 mL/min (assuming a constant medium viscosity of 0.7·10 -3 Pa s at 37 °C and = 61.14 · as previously described [33] ). Applied wall shear stress was quantified from the flow magnitude during the course of the experiment and tuned by adjusting the pump pressure.…”

“…Actin and collagen distributions were quantified with in-house developed software as described elsewhere. [33] Histological analysis: Fibrillar collagen and glycosaminoglycans (GAGs) at day 20 were visualized in cross-sections with the Picrosirius red stain and Alcian blue stain, respectively.…”

“…In the present study, motivated to improve the long-term clinical performance of in situ tissue engineered vascular grafts, we employ a human in vitro model to identify the mutual roles of physiological levels of shear stress and cyclic stretch on macrophage/fibroblast-mediated neotissue formation. Using our recently developed bioreactor, [33] we reveal that these loads differently regulate immune profiles, tissue growth, and matrix remodeling in co-cultures of (myo)fibroblasts and monocytes in electrospun vascular polycaprolactone bis-urea (PCL-BU) scaffolds. Whereas shear stress abrogates stretch-induced tissue growth and stimulates collageneous remodeling, cyclic stretch inhibits shear stress-driven secretion of proinflammatory cytokines (MCP-1 and IL-6).…”